Continuous logging of a person’s geographical position is required for various “life-log” applications, such as memory aids, automatic blog generation, and life pattern analysis. GPS is one way of logging, but it is unable to track movements indoors, and hence cannot track people ’s ordinary activities. We propose a WiFi-based location detection technology for location logging called LifeTag. It detects a device’s location from received WiFi beacon signals. It works indoors and outdoors, and its estimated accuracy is often comparable to that of GPS.We built WiFi-based location logging systems based on a smart phone and a keychain-like device using custom hardware. These prototypes record WiFi information every few minutes, and this information is converted into actual location logs. We describe some life patterns created by analyzing these location logs.We also discuss various application examples and ideas for when continuous location logging becomes commonplace.